1. Field of the Invention
The present invention relates to an optical scanning device which has deflection unit for deflecting, by a deflection mirror driven by a driving source, the travel direction of light emitted from a light source and which employs the light deflected by the deflection unit to perform optical scanning on an object to be scanned. The invention also relates to an image forming apparatus that includes the optical scanning device.
2. Description of the Related Art
Conventionally, an optical deflector disclosed in Japanese Patent Application Laid-open No. H6-51228 is known as deflection unit to be used for an optical scanning device of this type. The optical deflector allows a polygonal mirror shaped like a regular hexagonal prism to deflect the travel direction of a laser beam emitted from a laser light source, the polygonal mirror serving as a deflection mirror rotated by a drive motor acting as a driving source. In such a structure, the sound of wind produced by the rotating polygonal mirror may be turned into a noise. To reduce the wind noise, the optical deflector disclosed in Japanese Patent Application Laid-open No. H6-51228 is configured such that a resonance box which resonates at the resonance frequency that is the same as the frequency of the wind noise produced by the polygonal mirror is integrated with the housing that holds the polygonal mirror and the drive motor. This allows the wind noise produced by the rotating polygonal mirror to be attenuated by the resonance of the resonance box serving as a resonator, thereby preventing the noise from occurring due to the wind noise.
However, with this optical deflector, there was a possibility that an airflow produced by the rotation of the polygonal mirror hit the inlet of the resonance passage for guiding sound to the resonance space of the resonance box, thereby producing another noise like whistle sound (hereafter referred to as the whistle-like noise). In an attempt to reduce the whistle-like noise, provision of an additional resonance box having the same resonance frequency as the frequency of the whistle-like noise would lead to an increase in costs.
In view of the aforementioned background, there is a need to provide the following optical scanning device and an image forming apparatus that includes the optical scanning device. That is, provided is the optical scanning device which can avoid an increase in costs caused by an additional resonator to be provided to reduce a whistle-like noise while an increase in noise due to the whistle-like noise produced at the inlet of the resonance passage of the resonator is being avoided.